Author ORCID Identifier
0000-0001-7700-6169
Document Type
Dissertation
Date of Award
12-31-2022
Degree Name
Doctor of Philosophy in Environmental Science - (Ph.D.)
Department
Chemistry and Environmental Science
First Advisor
Mengyan Li
Second Advisor
Edgardo Tabion Farinas
Third Advisor
Alexei Khalizov
Fourth Advisor
Sara Casado Zapico
Fifth Advisor
Max M. Haggblom
Abstract
The spread of antimicrobial resistance in the environment and especially its transfer into human pathogens have emerged as global issues. Activated sludge units at municipal wastewater treatment plants are "hotspots" converging a multitude of contaminants, including antibiotics, antibiotic-resistant bacteria (ARB), human pathogens, and microplastics. The prevalence of antibiotics can induce stress response of sludge microbial communities and promote the development of new resistance mechanisms and transmission venues, through which the dissemination of antibiotic resistance genes (ARGs) arises as mediated by mobile genetic elements (MGEs). In this doctoral dissertation, the impacts of microplastics and genetic vectors (i.e., MGEs and bacterial hosts) on the mobility of ARGs are untangled to provide insights into the risk and management of antibiotic resistance derived at municipal wastewater facilities.
Considering microplastics as hubs that provide unique habitats to host ARB and human pathogens, in the first and second sections, multiple high-throughput sequencing techniques are employed to uncover microplastic-specific microorganisms and their potential roles in plastisphere (i.e., biofilms attached on microplastics). Polyethylene and polystyrene microplastics can significantly enrich ARGs, such as sul genes that confer resistance to sulfonamides, a major group of commonly used antibiotics. Furthermore, microplastics can selectively promote the proliferation of heterotrophic Novosphingobium, which are predicted as primary colonizers that facilitate biofilm formation, and antibiotic-resistant and pathogenic taxa (e.g., Raoultella ornithinolytica). The metagenomic binning analysis reveals that the PAC-sull-qacE?1-aadA2-intl1 cluster co-occurs with transposases and serves as a major genetic vector to spread these ARGs among Raoultella, Enterobacter cloacea, and Pseudomonas species in plastisphere. The third section is oriented to advance the knowledge of the spreading of an important sulfonamide resistance gene sadA, which encodes a flavin-dependent monooxygenase that enables sulfonamide degradation in the sludge. Notably, two sadA-carrying Gram-negative bacteria, Xanthobacter sp. LD2 and Lysobacter sp. RD1, are first identified and isolated from activated sludge samples. Though phylogenetically departed, their genomes harbor sadA genes that share high identity (>97.0%) to previously reported Actinobacteria species. This gene is embedded in a resistance cluster MerA-MerR-SRAP-sadA-Ycel within the composite transposon IS6100 on a plasmid of RD1. Mating experiments further demonstrate the horizontal transfer of sadA, implying a broad spectrum of sulfonamide-degrading bacteria in activated sludge. The fourth section focuses on analyzing the resistomes of 4 multidrug-resistant Chryseobacteria that are isolated from activated sludge in comparison with those (n = 211) from environmental, animal, and clinical origins. Though their genomes show no distinctive phylogenetic divergence, the resistance cluster of catB11-tetX encoding chloramphenicol and tetracycline inactivating enzymes is highly enriched in clinical isolates and collocates with recombinase and transposase genes. The resistance cluster is further found spreading across bacterial genera within the phylum Bacteroidota, revealing potential health risks as some of these hosts are human pathogens associated with a myriad of nosocomial infections.
Recommended Citation
Pham, Ngoc Dung, "Microplastics and genetic vectors promoting the dissemination of antimicrobial resistance in municipal wastewater treatment processes" (2022). Dissertations. 1922.
https://digitalcommons.njit.edu/dissertations/1922
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